Chronic Cannabis Use May Cause Brain Inflammation

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Chronic marijuana use may cause inflammation in the brain that
leads to problems with coordination and learning, a new study in
animals suggests.

The study also teased out why this brain inflammation leads to
motor and learning problems, and found a surprising answer —
cannabis activates immune cells that appear to play a critical
role in how a brain region called the cerebellum works.

In the study, mice were given delta9-tetrahydrocannabinol, or
THC,
the active ingredient of marijuana, for six days. Then the
mice were required to perform several tasks to test their
coordination, as well as their ability to learn to associate a
sound with a puff of air to the eye. During the latter task,
called eyeblink conditioning, mice should learn to anticipate the
air puff, and blink when they hear the sound.

Mice given THC showed impairments in both tasks. (A previous
study in people also found that cannabis users had trouble in an
eyeblink conditioning task.)

The researchers also found that THC activated microglial cells,
which are immune cells in the cerebellum. These microglial cells
then induced inflammation in the cerebellum, which resulted in
the learning and coordination problems.

These problems went away when the researchers used a drug to
prevent activation of microglial cells. This result could offer
"interesting new therapeutic approaches for treating these
cannabis-induced
side effects, the researchers write in the July 1 issue of
the Journal of Clinical Investigation..

Study researcher Andrés Ozaita, of the Universitat Pompeu Fabra
in Barcelona, noted that these side effects typically go away
when the mice are no longer exposed to THC.

Chronic use of marijuana is known to lower the number of
cannabinoid receptors (receptors that bind to THC) in the brain.
The reduced number of receptors is what appears to eventually
lead to the activating of the microglial cells, Ozaita said.

More research is needed to determine what kinds of problems these
"cerebellar deficits" cause people to have in everyday life,
Ozaita said. It's possible that microglial cell activation in the
cerebellum causes hard-to-detect problems — such as a slightly
delayed reaction time while driving — that researchers wouldn't
know about unless they tested for them, he said.